Steel is the generic name for a group of ferrous metals, composed principally of iron, which have considerable durability and versatility. It is used as a base material for many commercial applications, including for example, major appliances and industrial equipment. One of the problems which arise in the use of steel, including stainless steel, is its corrosion and staining, either by the atmosphere or by the environment in which it is used. Corrosion refers to destruction, degradation or deterioration of the metal due to reactions of the material and its environment. The rate of corrosion may vary, depending on the surrounding conditions and also the composition of the steel. Stainless steel, for example, is more resistant to corrosion than plain carbon and other steels. This resistance is due to the addition of chromium to alloys of iron and carbon. Although stainless steel has appreciable resistance to corrosion, it will still corrode in certain circumstances and attempts have been made to prevent or reduce this corrosion.
Corrosion inhibitors can be used to inhibit the corrosion of ferrous metals and provided in cleaning compositions. Many metallic ion corrosion inhibitors have been used alone or in combination in various chemical treatment formulations. Some inhibitors, however, have been found to be toxic and/or detrimental to the environment. Inorganic phosphates such as orthophosphate and pyrophosphate have been widely used corrosion inhibitors. However, the inorganic phosphates have been found to contribute to scale formation (e.g., calcium phosphate, iron phosphate and zinc phosphate salts). Some organic phosphonates (e.g. 2-phosphono-butane-1,2,4-tricarboxylic acid (PBTC), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), and aminotrimethylene-phosphonic acid (AMP)) have been used as corrosion inhibitors; however, the effectiveness has not been optimized. Some hydroxycarboxylic acids (e.g. gluconic acid) have also been used as corrosion inhibitors in aqueous applications such as cleaning cooling towers; however, there are microbiological growth control concerns and performance concerns when used in certain conditions, such as high alkalinity, temperature and/or oxidizing environments.
There is a need for corrosion inhibition using highly alkaline cleaning compositions, such as those commonly used in clean-in-place (CIP) applications. CIP applications are required in many industrial applications, such as the manufacture of foods and beverages, where hard surfaces commonly become contaminated with soils such as carbohydrate, proteinaceous, and hardness soils, food oil soils and other soils. Food and beverage soils are particularly tenacious when they are heated during processing (e.g. in dairy plants, dairy products are heated on a pasteurizer such as a high temperature short time pasteurizer or ultra-high temperature pasteurizer). Also, many food and beverage products are concentrated or created as a result of evaporation. When that surface is a heat exchange surface, the soil becomes thermally degraded rendering it even more difficult to remove. Over time, the layer of soil increases in thickness as more food or beverage product is passed over the heat exchange surface. The layer of soil acts as an insulator between the heat and the product being heated, thereby reducing the efficiency of the heat exchange surface and requiring more energy to create the same effect if the heat exchange surface were clean. When the heat exchange surface is an evaporator, the difference between a clean heat exchange surface and a soiled heat exchange surface can mean the difference in millions of dollars in energy costs for an evaporator plant. With the cost of energy increasing significantly, as well as an increased awareness of protecting the environment by preserving natural resources, there remains a need for cleaning programs that can clean heat exchange surfaces and create an efficient transfer a heat.
Surfaces cleaned in a CIP process are most often stainless steel surfaces. The cleaning requires a complete or partial shutdown of the equipment being cleaned, which results in lost production time. Many times, the equipment is not thoroughly cleaned, due to the large downtime needed. Therefore, what is needed is an improved method for cleaning this equipment, using the CIP process, which uses an alkaline cleaning composition that will prevent corrosion and damage to the stainless steel surfaces treated in order to thoroughly remove the soils. It is against this background that the present invention has been made.
It is an object of this invention to provide aqueous, highly alkaline cleaning compositions that are noncorrosive to stainless steel and other metal surfaces due to addition of a corrosion inhibitor such as gluconic acid, sodium gluconate and/or salts thereof.
It is a further object of this invention to provide such corrosion inhibited highly alkaline cleaning compositions that do not stain the treated surfaces as a result of the formulation using a corrosion inhibitor.
Accordingly, it is an object of this invention to provide non-staining, corrosion inhibited highly alkaline cleaning compositions effective in both liquid and vapor phases for treatment of metal surfaces, such as CIP processes.
Yet another object is to provide a liquid phase and vapor phase alkaline cleaning composition having corrosion and stain inhibition suitable for use with stainless steel.
Other objects, aspects and advantages of this invention will be apparent to one skilled in the art in view of the following disclosure, the drawings, and the appended claims. These and other embodiments will be apparent to these of skill in the art and others in view of the following detailed description. It should be understood, however, that this summary and the detailed description illustrate only some examples, and are not intended to be limiting to the invention as claimed.